Toolbox Talks

Valve Cap Thread Sealing

An engineer narrowly escaped serious injury when a valve cap that he was removing from a stop valve exploded out of his hand with a loud bang and shot across the plant room.

The incident happened because the previous person to replace the cap had sealed the threads with a combination of PTFE tape and red silicone sealant. This tape and sealant prevented gas, which had accumulated in the cap, from being released safely through the vent hole or down the threads, as it was undone. Consequently, as the cap came off the last thread, there was a sudden release of gas, which blew the cap out of the engineer's hand.

On this occasion the cap was at low level and contained gas. But it could just as easily have been at eye level, or contained some liquid, the consequences of which could have been much worse.

For your own safety and that of others:

• Never seal a valve cap with anything but the correct seal ring.

• Do not use the cap as a means of preventing a leak - fix the leaking valve stem seal.

• Wear eye protection when opening any refrigerating system component.

• Wear impervious gloves to prevent refrigerant contacting the hands.

• Use a suitable spanner.

• Remove seal caps slowly, in case refrigerant is present in the cap.

• NEVER APPLY EXTERNAL HEAT TO A VALVE CAP.

• Before the cap is refitted, check that the vent hole and threads are clean and not obstructed by ice, grease, dirt. If necessary low temperature oil may be used to lubricate the threads.